When ants kiss, it's all about the chemistry

Ants aren't the only critters to exchange fluids through this process, known as trophallaxis(Credit: Adria LeBoeuf)

Master organizers, builders and farmers, ants have developed some pretty nifty ways to share resources and help the colony thrive. One example of this is a mouth-to-mouth encounter known as trophallaxis, which they use to pass food to one another. If that sounds like an extreme way to feed the family, then you might be right. Scientists have discovered that there is much more at play when these incestuous insects lock lips, using it as an opportunity to pass on important chemical messages that shape the colony's next generation.

"A lot of researchers consider trophallaxis only as a means of food-sharing," says Professor Richard Benton of the Center for Integrative Genomics at Switzerland's University of Lausanne. "But trophallaxis occurs in other contexts, such as when an ant is reunited with a nest-mate after isolation. We therefore wanted to see if the fluid exchanged by trophallaxis contains molecules that allow ants to pass other chemical messages to each other, and not just food."

So the team collected fluid samples from Florida carpenter ants engaging in trophallaxis and used mass spectrometry and RNA sequencing to analyze the contents. It found that the fluid contained a large number of proteins that appear to regulate the growth of ants, and high levels of a juvenile hormone that plays a key role in insect development, reproduction and behavior.

To quantify how much of a role exactly, the team slipped the hormone into the food of larvae-rearing ants and tracked the results. As it turns out, the larvae reared with the supplemented hormone levels were twice as likely to reach adulthood. The team says that the ants appear to selectively deliver the hormones to shape the future and address shortcomings in the colony's population.

"This indicates that juvenile hormone and other molecules transferred mouth-to-mouth over this social network could be used by the ants to collectively decide how their colony develops," says LeBoeuf. "So, when the ants feed their larvae, they aren't just feeding them food, they are casting quantitative ballots for their colony, administering different amounts of growth-promoting components to influence the next generation."

And because ants aren't the only critters to exchange fluids through trophallaxis, with termites, bees and wasps some other examples, the discovery raises the possibility that similar processes are at play in other social insects, and perhaps in other animals as well.

"Overall, we show that liquid transmitted among ants contains much more than food and digestive enzymes," says study lead author Adria LeBoeuf. "Our findings suggest that trophallaxis underlies a private communication channel that ants use to direct the development of their young, similar to milk in mammals. More generally, this opens the possibility that the oral exchange of fluids, such as saliva, in other animals might also serve previously unsuspected roles."

The research was published in the eLife.

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